Talks stalled on wages, pension and insurance, said Frank Larkin, a spokesman for the International Association of Machinists and Aerospace Workers. Other issues, such as work rules, have been addressed, he said.

The action comes as United strives to move past operational problems that punished the carrier's customers last summer. The Department of Transportation reported Thursday that United's on-time performance nearly returned to normal in September, though the airline continues to trail the rest of the industry.

About 700 mechanics at Denver International Airport are prepared to strike, said Scott Brown, an officer with the local branch of IAM District 141-M. That can't happen, however, until after a federal mediator calls off the talks, which has not occurred.

"We don't believe United is negotiating in good faith. They aren't working toward getting this thing resolved anytime soon," Brown said.

"The pilots approved their contract last week, and it was very generous. We expected after that the company would be aggressive in getting our contract done, but they're not doing that," he said.

United officials said in a statement that the negotiations "have become exceptionally difficult." "We continue to believe that with hard work on both sides, progress can be made, and therefore we hope that the IAM will resume discussions as soon as possible," the company said.

The union wants United to bring higherranking officials to the table or authorize its negotiators to make decisions on wage issues.

"Until this company gets serious and places officials at the bargaining table who are able to complete these negotiations, we're wasting our time here," said Scotty Ford, lead negotiator for the mechanics.

The IAM also represents about 30,000 ramp workers, customer service agents and reservations personnel. Negotiations for that group are separate and have so far proceeded without federal mediation.

The mechanics called in a federal mediator about two months ago. Larkin said little or no progress on the key "economic package" has been made since then.

United faces similar problems with its 25,000 flight attendants, including 1,700 in the Denver area. The flight attendants' union is renegotiating its contract with the airline and has set a Saturday deadline.

Flight attendants held rallies and informational picketing Thursday at 40 airports worldwide where United has significant operations. At DIA, 40 to 50 workers handed out information to passengers on the sixth-level entrance to the main terminal's west side.

If the airline doesn't make an acceptable offer by Saturday, the union will begin actively opposing United's proposed merger with US Airways, said Sheri Meehleis, head of the local union.

United's labor problems began in April, when its 10,500 pilots began refusing overtime during contract negotiations. United's on-time performance and cancellations hit the lowest levels in the carrier's history in July and August. A tentative contract with the pilots' union was reached in late August and approved by pilots last week.

The Department of Transportation reported Thursday that United's performance bounced back after the agreement was reached. The airline landed 71.8 percent of its flights within 15 minutes of their scheduled arrival time in September, up from 42.7 percent a month earlier.

Trans World Airlines was the best performer in September, landing 85.5 percent of its flights on time. US Airways was second worst, with 75.1 percent of its planes landing on time.

In March, before labor issues arose, United landed 73.5 percent of its flights on time. At DIA, where United and its Express carriers fly nearly 70 percent of passengers, the improvement was noticeable. The airport reported a 78.4 percent on-time figure for September, above average for the nation's top airports and up from 53.2 percent in August.

"We're doing much better than we were this summer, but obviously we have a long way to go," said United spokesman Joe Hopkins. "That's a challenge we're attending to."

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